Reduction of aromatic nitrogen compounds



Patented July 20, 1 954 REDUCTION OF AROMATIC NITROGEN COMPOUNDS Allen Walter Sogn, Buffalo, N. Y., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York No Drawing. Application January 8, 1952, Serial No. 265,538

I 22 Claims. 1

This invention relates to improvements in the alkaline reduction of aromatic nitrogen compounds containing nitrogen in a reducible form as a nuclear substituent. It relates more particularly to improvements in the process of effecting the reduction, by means of alkaline reducing agents, of such aromatic nitrogen compounds, and especially mononuclear aromatic nitrogen compounds of saidtype, in which the nitrogen is at a higher stage of oxidation than the hydrazo stage.

The alkaline reduction of aromatic nitrogen compounds containing nitrogen in a reducible form is well known. Thus it is known to reduce aromatic nitro compounds, aromatic nitroso compounds, aromatic azoxy compounds, aromatic azo compounds and aromatic hydroxylamino compounds by means of alkaline reducing agents. It is also known that the extent to which the reduction can be carried depends on the strength of the reducing agent and the severity of the reduction conditions.

For example, it is known to reduce nitrobenzene with a metal alcoholate, and especially an alkali metal alcoholate. The reduction is usually carried out by heating nitrobenzene with-alcoholic caustic alkali (e. g., sodium hydroxide and an alcohol) at the boiling ointof the mixture while refluxing at atmospheric pressure. Alkali metal hydroxide and an alcohol are used instead of the equivalent preformed alcoholate because of lower cost. Methanol is preferred as the. alcohol in view of its relative cheapness. The reduction product, aside from a small amount of aniline, is azoxybenzene; the alkali metal alcoholates are not sufiiciently strong reducing agents to carry it with sodium or potassium hydroxide and methanol under more elevatedtemperatures and pres-,

sures, such astemperaturesof' 140 to 180 C. and pressures ofofmore'latmospheres. Such a procedure has the usual disadvantages of operation under pressure, as; well as requiring expensive pressure apparatus.

Thus, the production of aromatic azo and hydrazo'compounds from aromatic nitro compounds 2 and their intermediate reduction products presents a number of problems from the standpoint of commercial practice.

A primary object of the present invention is to provide improvements in the alkaline reduction of reducible aromatic nitrogen compounds of the type referred to above (i. e., containing nitrogen in a reducible form as a nuclear substituent), whereby the reducing power of metal alcoholate reducing agents and especially of alcoholic caustic alkali reducing agents is enhanced and other advantages are secured.

Other objects of the present invention are to provide a process for the production of aromatic azo compounds in good yields by the reduction of aromatic nitro compounds, and their reduction products up to and including azoxy compounds, with metal alcoholates under moderate reaction conditions and in simple apparatus; to

provide a process for the production of aromatic hydrazo compounds by reduction of aromatic nitro compounds and other reducible aromatic nitrogen compounds with metal alcoholates under moderate conditions and in simple apparatus; and to provide improvements in the reduction of reducible aromatic nitrogen compounds with metal alcoholates whereby the evolution of hydrogen gas during the reduction is suppressed. y

Additional objects in part will be obvious and in part will appear hereinafter.

In my application Serial No. 184,123, filed Sep tember 9, 1950, now Patent No. 2,645,636, I have disclosed and claimed the improvement in the method of reducing reducible aromatic nitrogen compounds by the action of metal alcoholates which comprises'carrying out the reduction in reaction mixtures in which reduction promoters of a novel class have been incorporated, namely, naphthoquinoid compounds.

According to the present invention, the foregoing objects are accomplished by carrying out the reduction of a reducible aromatic nitrogen compound by means of a metal alcoholate in a reaction mixture containing a reduction promoter of another novel class.

The class of reduction promoters employed in accordance with the present invention, which class is designated herein by the expression quinoid hydroxynaphthalene compounds, consists of the hydroXy-naphthalenes having a total of at least two nuclear substituents of which not more than two are hydroxyl groups and of which substituents two are in the same benzene ring of the naphthalene nucleus in quinoid relation to each other, one of said substituents in quinoid relation being a hydroxyl group and the other of said substituents in quinoid relation being a hydroxyl group or an amine radical. As employed herein, the term amine radical denotes generically the amino group (Nl-I2), monoalkylamino g r o u p s monophenylamino groups and acylamino groups.

Thus, said class of quinoid hydroxynaphthalene compounds includes:

1, l-dihydroxy-naphthalene 4-aminol-hydroxy-naphthalene i-arnino-l-hydroxy-naphthalene-2-sulfonic acid 2-amino-l-hydroxy-naphthalene 2,S-dihydroxy-naphthalene 2,3-dihydroxy-naphthalene-fi-sulfonic acid 1-amino-2-hydroxy-naphthalene l-amino-2-hydroxy-naphthalene-4-sulfonic acid l-phenylamino-l-hydroxynaphthalene I have discovered that the presence in the reaction mixture of a small amount of a quinoid hydroxynaphthalene compound, such as 1,4-dihydroxy-naphthalene, has a modifying effect upon the reduction, as a result of which a number of benefits may be secured.

Thus, as compared with a reduction carried out under the same conditions but in the absence of the quinoid hydroxynaphthalene compound, the speed of the reduction is increased and/or products of a higher state of reduction are obtained, without substantial sacrifice of the total yield of reduction products secured from the starting material. In the reduction of aromatic nitro compounds, the presence of a quinoid hydroxy-naphthalene compound in the metal alcoholate reaction mixture makes possible the obtainment of azo compounds directly, without requiring the use of drastic operating conditions, such as high temperatures and pressures of or more atmospheres. Similarly, the presence of a quinoid hydroxynaphthalene compound in the reaction mixture makes possible the production of hydrazo compounds from nitro, azoxy and azo compounds by means of metal alcoholate reducing agents without requiring the use of drastic operating conditions. By their presence, the quinoid hydroxynaphthalene compounds suppress almost completely side reactions leading to the evolution of hydrogen gas during the reduction, thereby greatly increasing the safety of the reduction process and minimizing waste of the reducing agent.

Where no substantial change in the degree of reduction is desired, the presence of a quinoid hydroxynaphthalene compound in the reduction reaction medium makes possible the use of milder reaction conditions or the use of decreased amounts of reducing agent. Thus, in the reduction of an aromatic nitro compound with sodium hydroxide and methyl alcohol, the presence of a quinoid hydroxynaphthalene compound in the reaction mixture makes possible the use of a lesser amount of sodium hydroxide, thereby decreasing the cost of the operation.

Of the quinoid hydroxynaphthalene compounds, those which are para-quinoid hydroxynaphthalene compounds (that is, in which a hydroxyl group is in lA-position relative to a second hydroxyl group or an amine radical) are preferred for use in the reduction of reducible aromatic nitrogen compounds by means of metal alcoholates. lA-dihydroxynaphthalene and 4- amino-1hydroxy-naphthalene are especially preferred in view of their outstanding activity as reduction promoters coupled with their availability and relatively low cost.

In the practice of the present invention, the reducible aromatic nitrogen compound is subjected to the reducing action of a metal alcoholate reducing agent in a reaction mixture containing one or more quinoid hydroxynaphthalene compounds as a reduction promoter. In the pre ferred practice of the invention, wherein a reducible aromatic nitrogen compound is heated with a caustic alkali and an alcohol (preferably sodium hydroxide and methanol) at the boiling point of the reaction mixture, the quinoid hydroxynaphthalene compound is preferably mixed with the alcohol and, after adding the caustic alkali and heating, the nitrogen compound to be reduoed is added to the mixture.

The quinoid hydroxynaphthalene compound may be added to the reaction mixture in various ways and at various times, however, without departing from the scope of the invention. If desired, it can be preformed separately and added to the reaction mixture or it can be formed in the reaction mixture, for example, by reaction of an acid salt of an amino-hydroxy-naphthalene (such as, the hydrochloride) with the caustic alkali.

The quinoid hydroxynaphthalene compound can be employed in various amounts. It is a feature of the present invention that only small amounts of the quinoid hydroxynaphthalene compounds are required. Thus, amounts lying Within the range 9, to mol of quinoid hydroxynaphthalene compound per mol of reducible aromatic nitrogen compound are ordinarily employed. The minimum amount required to produce a significant reduction-promoting effect varies with the individual quinoid hydroxynaphthalene compound, the nature of the reducible aromatic nitrogen compound, and the reaction conditions. In generaLa greater reduction-promoting effect is secured by increasing the amount of quinoid hydroxynaphthalene compound employed and a lesser effect results from decreasing the amount employed, other reaction conditions being constant. Amounts greater than mol of quinoid hydroxynaphthalene compound per mol of reducible aromatic nitrogen compound usually are not advantageous, although they may be used if desired, since the additional benefits derived therefrom are not of sufiicient commercial importance to compensate for the increased cost of the extra amount of quinoid hydroxynaphthalone compound.

The invention will be illustrated by the following specific examples, but it is to be understood that it is not limited to the details thereof and that changes may be made without departing from the scope of the invention. The temperatures are in degrees centigrade and the parts are by weight, unless designated as parts by volume in which case the amount signifies the volume occupied lay-" the same number of parts by weight of water at 4 C.

Example 1 Part A.360 parts of methanol and 6 parts of 1,4-dihydroxy-naphthalene were charged to a flask equipped with a reflux condenser, agitator, dropping funnel and thermometer. 446 parts of solid sodium hydroxide were then added over the course of 15 minutes. The mixture was heated to refluxing, 738 parts of nitrobenzene were added, and the reaction mass was boiled and refluxed (about to for 20 hours under: atmospheric pressure. A negligibleamount ofgas was. evolved duringthe addition of nitro: benzene and subsequent reflux period. Unreacted methanolwas then removed by distillation with live steam, afterwhic-h the mass was allowed to stand and separate into an upper oil phaseanda lower aqueous phase. The aqueous phase, consisting essentially of sodium hydroxide and sodium. formate in solution, was drawn off at about 100 and the oil phase was clarified by filtration from a small amount of'black insoluble residue. The resulting oil, which contained less than 1% of moisture partially emulsified therein, consisted essentially of a mixture of 63.5% of azobenzene and 36.5% of azoxybenzene. After being dried over calcium chloride, it had a setting point of 506. The yield was 516 parts, which corresponds to a combined yield of a20- benzene and azoxybenzene of 91.5% of the theoretical, based onthe nitrobenzene charged.

Pa'rt B.The process of part A was repeated without addition of the lA-dihydroxy-naphthalene. 25,000 parts by volume of hydrogen were evolved and the oil product, which amounted to 573 parts, consisted essentially of azoxybenzene (it had a setting point of 33.5). This corresponds with a yield of about 96% of the theoretical yield of azoxybenzene.

Example 2 570 parts of methanol, 540 parts of caustic soda flakes and 20 parts of 1,4-dihydroxynaphthalene were charged to a flask equipped with a reflux condenser, agitator, dropping funnel and thermometer. The mixture was heated to boiling and 738 parts of nitrobenzene were added to the refluxing mass during 2 hours. The reaction mass thus obtained was boiled and refluxed (tem perature 92 to 93) for 19 hours under atmospheric pressure, after which 178 parts (225 parts by volume) of methanol were distilled from the mixture, thereby raising its reflux temperature to 99. The resulting concentrated reaction'mixture was refluxed for 20 hours under atmospheric pressure to complete the reduction reaction. Unreacted methanol was then removed by distillation with live steam, during which the tempera" ture was kept below 110 by addition of water, as required. The aqueous mixture thus obtained was cooled to 60 and filtered, and the filter cake of hydrazobenzene was washed free from alkali with cold water, sucked dry, and air dried at room temperature. The dry product thus obtained melted at 125.5", indicating that it was hydrazobenzene of good purity. The yield was 541 parts, which correspond to 98% of the theo retical yield of hydrazobenzene, based on the nitrobenzene charged.

Example 3 The procedure described in Example 1, part A, was repeated, using 6 parts of 4-amino-l-hydroxynaphthalene hydrochloride in place of the 1,4 dihydroxy-naphthalene. The product weighed 510 parts and consisted essentially of a mixture of azobenzene and azoxybenzene (setting point of 46.4"). This corresponds with a yield of about 90% of the theoretical, based on the nitrobenzene charged.

Example 4 The procedure described in Example 1, part A, was repeated, using 12 parts of Z-arnino-lhydroxy-naphthalene hydrochloride in place of the 1,4dihydroxynaphthalene. The product weighed 522 parts and consisted essentially of a mixtureof azobenzene: and azoxybenzene. (setting pointof A6") This-corresponds with a yield of' about 92.5%. of thetheoreticaL. based on the nitrobenzene charged.

Example 6 The procedure described in Example 1, part A, was repeated, using 18 parts of l-amino 2- naphthol-4-sulfonic acid in place of the 1,4-dihydroxyrnaphthalene. The product weighed 552 parts and consisted essentially of a mixture of azobenzene and azoxybenzene (setting point of 36.59). This corresponds with a yield of about 96.5% of the,- theoretical, based on the nitrobenzene charged.

As noted above, 'the invention is not limited to the details of the foregoing illustrative examples, and changes can be made without departing from the scope of the invention.

Thus, the process is applicable to the reduction of other aromatic nitrogen compounds containing nitrogen in a reducible form as a nuclear substituent, as for example, o-nitrotoluene, mnitrotoluene, o-nitrochlorobenzene, m-nitro chlorobenzene, o-nitrophenetole, o-nitrobenzoic acid and o-nitrobenzene sulfonic acid. In view of the extensive use of hydrazobenzene and its o-substituted derivatives (such as o,o-dichlorohydrazobenzene, o,o'-hydrazotoluene, o,o-hydra zoanisole, 0,0-diethoxy-hydrazobenzene, etc.) as intermediates for the manufacture of benzidine and related derivatives of benzidine, the process of the present invention is of special value as a means for reducing the cost of manufacturing such hydrazo compounds from the corresponding reducible mononuclear aromatic nitrogen com pounds (such as, nitrobenzene and its o-substituted derivatives and reduction products thereof) in which the nitrogen is at a higher stage of oxidation than the hydrazo stage.

The reduction of aromatic nitro compounds to azoxy compounds 1) of azoxy compounds to azo compounds (2), and of azo compounds to hydrazo compounds (3) proceeds according to the following equations, in which R is an aromatic nucleus:

I 2R-NNR 8HCOONa 61120 2RNNR onion NaOH (3) 2RN=N'R HCOONa 21120 2RN=NR onion NaOH 2RNHHNR H COONa In carrying out the reduction by means of sodium hydroxide and methanol, it is preferable to employ these reagents inamounts in excess of those theoretically required. Extra methanol over that theoretically required is generally desirable for use as a solvent, and an additionalexcess is'desirable to counteract the diluting effect of the water generated'in accordance with above Equations 1 and 2, which would otherwise tend to retard the reaction. An excess of sodium hydroxide also is desirable since it tends 'to'im crease the rate of reaction.

It is possible to carry the reduction of a par ticular reducible aromatic nitrogen compound to various stages, dependin upon'the amounts of sodium hydroxide and methanol, as well as the nature and amount of quinoid hydroxynaphthalene compound, employed. For example, nitrobenzene may be reduced to hydrazobenzene in a single reaction mixture, as illustrated in Example 2, or nitrobenzene may be reduced to azoxyand/or azobenzene in one reaction mixture, as illustrated in the other above examples, and the resulting azoxybenzene and/or azoberrzene then isolated and reduced to hydrazobenzene with a fresh charge of sodium hydroxide and methanol.

fhe temperature at which the reaction is carried out also may be varied although, in the reduction performed with the aid of alcoholic caustic alkali, temperatures at or near the boiling point of the reaction mixture at atmospheric pressure (ordinarily about 90 to 105 C.) are preferred. At lower temperatures, the reaction is slower, under otherwise similar conditions, and may require an excessively long time to produce the same results as the preferred temperatures. Conversely, higher reaction temperatures result in a short time cycle but require the use of closed reaction vessels. However, temperatures greatly exceeding 110 0., though not precluded, are less desirable; since even in the presence of the quinoid hydroxynaphthalene promoters they lead to evolution of considerable amounts of hydrogen gas and formation of primary amines, with consequent loss of yield of the desired reduction products.

While for economical and simple operation it is preferred to use, as-a solvent or diluent of the reaction mixture, an excess of the alcohol em ployed for the alcoholate, the invention is not limited thereto. Thus, other solvents and diluents can be employed; for example, the process may be carried out with amounts of sodium hydroxids and methanol only slightly in excess over the amounts theoretically required for the reduction in a, reaction medium containing a sufficient amount of xylene to provide a stirrable reaction mass. Instead of xylene, other inert solvents ordiluents may be used, such as benzene, toluene, monoand dichlorobenzenes. Further, while it is simpler to employ, as the solvent or diluent, an excess of the alcohol functioning as a reducin agent, other alcohols can be employed; also mixtures of alcohols can be used, especially where it is desirable to modify the boiling temperature of the reaction mixture.

As a matter of convenience and for economical operation, the process is generally carried out by forming a metal alcoholate in the reaction mixture; for example, by reacting caustic alkali with the alcohol. If desired, however, preformed metal alcoholates may be employed as reducing agents, in which case the diluting efiect of the water formed as a'by-product of the reaction of caustic alkali with the alcohol is avoided.

Sodium hydroxide and methanol are employed in the specific'examples in View of their relatively lower cost and ready availability. The invention'is not limited thereto, however, and other alkalis' (for example, potassium hydroxide) and other alcohols "(for example, ethyl" alcohol'and the various' propyl, butyl and higher alcohols) may be employed,if desired.

The products-of the-reduction'can be isolated from the reaction mixtures in any suitable manner. Aside from those cases in which the reaction mixture contains an insoluble residue resulting from the'presence of a quinoid hydroxynaphthalene compound in the reaction mixture, the isolation of the reduction products can be carried out inthe usual manner.

Thus, for example, the reaction mixture may be cooled to crystallize the reduction product and filtered, and the cake washed with water to remove alcohol, sodium formate formed as abyproduct of the reduction, and sodium hydroxide. Generally, it is preferred to steam distill the methanol (and dehydrate the aqueous methanol thus obtained, by fractional distillation for reuse in subsequent reactions) and then cool the remaining hot-aqueous mass to crystallize the reduction product, which maybe washed as usual with water. Where the product is'molten in the hot mixture, as in the case of azoxyandazobenzenes, it-is simpler to stratify the mass into an aqueous phase and an oil phase,- whereupon the latter can be readily separated as illustrated in the examples.

lhe quinoid hydroxynaphthalene compounds are generally soluble in the aqueous and/ or alcoholic layer noted above,- and thus can be separated from the reduction product. When the use of a quinoid hydroxynaphthalene compound produces a small amount of insoluble by-product, it may be removed in any suitable manner, as by filtering the hot mixture prior to the phaseseparation, or as illustrated in the examples.

Any other members of'the class of quinoid hydroxynaphthalene compounds, and especially those specifically disclosed above, maybe substituted for the reduction promoters employed in the above. illustrative examples.

I claim:

1. The improvement'in the method of reducing an aromatic nitrogen compoundcontainingnitrogen in-a reducible form as a nuclear substituent at a higher stage of oxidation than the hydrazo stage by the action of a metal alcoholate, which comprises carrying out the reduction in a reaction mixture in which a quinoid hydroxynaphthalene compound has been incorporated, whereby the reduction of the-aromatic nitrogen compound is promoted.

2. A method as defined in claim 1, which comprises heating the aromatic nitrogen compound with a reducing mixture ofan alkali metal hydroxide and a lower alcohol in a reaction mixture containing a quinoid hydroxynaphthalene compound in an amount corresponding with to mol per mol of aromatic nitrogen compound.

3. A method as defined in claim 1, wherein the nitrogen is a substituent in a benzene nucleus, the metal alcoholate'is an alkali metal alcoholate, and the hydroxnaphthalene compound is a paraquinoid hydroxynaphthalene "compound.

4. A method as defined in claim 3, wherein at least 5 mol of the para-quinoid hydroxynaphthalene compound is incorporated with the reducing mixture of alkali metal hydroxide and lower alcohol, and the aromatic nitrogen compound is heated with the resulting mixture.

5. A method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage and selected from the group consisting of nitrobenzene, an ortho-substituted nitrobenzene, and reduction products thereof, which comprises heating the aromatic nitrogen compound with a reducing mixture of an alkali metal hydroxide and a lower alcohol in a reaction mixture in which a small amount of a quinoid hydroxynaphthalene compound has been incorporated, whereby the reduction of the aromatic nitrogen compound is promoted.

6. A method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage and selected from the group consisting of nitrobenzene, an ortho-substituted nitrobenzene, and reduction products thereof, which comprises heating the aromatic nitrogen compound with a reducing mixture of sodium hydroxide and a lower alcohol in a reaction mixture containing a hydroxynaphthalene having a total of at least two nuclear substituents or" which not more than two are hydroxyl groups and of which substituents two are in the same benzene ring of the naphthalene nucleus in quinoid relation to each other, one of said substituents in quinoid relation being a hydroxyl group and the other of said substituents in quinoid relation being selected from the group consisting of hydroxyl and amino, whereby the reduction of the aromatic nitrogen compound is promoted.

7. A method as defined in claim 6, wherein the hydroxynaphthalene is a hydroxynaphthalene having a total of at least two nuclear substituents of which two are hydroxyl groups which are in the same benzene ring of the naphthalene nucleus in quinoid relation to each other.

8. A method as defined in claim 6, wherein the hydroxynaphthalene is a 1,4-dihydroxy-naphthalens as a reduction promoter.

9. A method as defined in claim 6, wherein the hydroxynaphthalene compound is a hydroxynaphthalene having a total of at least two nuclear substituents of which one is a hydroxyl group and another is an amino group, said hydroxyl and amino groups being substituents in the same benzene ring of the naphthalene nucleus in quinoid relation to each other.

'10. A method as defined in claim 6, wherein the hydroxynaphthalene compound is a 4-amino-1- hydroxy-naphthalene.

11. A method as defined in claim 4, wherein the aromatic nitrogen compound is heated with a reducing mixture of sodium hydroxide and methanol containing a small amount of a hydroxynaphthalene having a total of at least two nuclear substituents of which not more than two are hydroxyl groups and of which substituents two are in the same benzene ring of the naphthalene nucleus in quinoid relation to each other, one of said substituents in quinoid relation being a hydroxyl group and the other of said substituents in quinoid relation being selected from the group consisting of hydroxyl and amino.

12. A method as defined in claim 6, wherein the aromatic nitrogen compound is heated with sodium hydroxide and methanol in a reaction mixture containing a small amount of 1,4-dihydroxy-naphthalene.

13. A method as defined in claim 6, wherein the aromatic nitrogen compound is heated with sodium hydroxide and methanol in a reaction mixture containing a small amount of 4-amino-1- hydroxy-naphthalene.

14. A method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage and selected from the group consisting of nitrobenzene, an ortho-substituted nitrobenzene, and reduction products thereof, which comprises mixing a small amount of a quinoid hydroxynaphthalene compound with a lower alcohol, adding sodium hydroxide, and heating the aromatic nitrogen compound with the resulting reaction mixture.

15. A method as defined in claim 14, wherein the aromatic nitrogen compound is nitrobenzene, the alcohol is methanol, and the quinoid hydroxynaphthalene compound is a para-quinoid hydroxynaphthalene compound.

16. A method as defined in claim 6 wherein an amount of the hydroxynaphthalene corresponding with at least mol per mol or aromatic nitrogen compound is incorporated with a reducing reaction mixture containing sodium hydroxide and methanol, and the aromatic nitrogen compound is heated with the resulting reaction mixture.

17. A method as defined in claim 16 wherein the aromatic nitrogen compound is nitrobenzene and the hydroxynaphthalene is 1,4-dihydroxynaphthalene.

18. A method as defined in claim '16 wherein the aromatic nitrogen compound is nitrobenzene and the hydroxynaphthalene is 4-amino-l-hydroxy-naphthalene.

19. A method as defined in claim 16, wherein the aromatic nitrogen compound is nitrobenzene and the hydroxynaphthalene is l-amino-Z-hydroxy-naphthalene.

20. A method as defined in claim 16, wherein the aromatic nitrogen compound is nitrobenzene and the hydroxynaphthalene is 1-amino-2-hy droxy-naphthalene-4-sulfonic acid.

21. A method as defined in claim 16, wherein the aromatic nitrogen compound is nitrobenzene and the hydroxynaphthalene is Z-amino-l-hydroxy-naphthalene.

22. A method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage and selected from the group consisting of nitrobenzene, an ortho-substituted nitrobenzene, and reduction products thereof, which comprises heating the aromatic nitrogen compound with an alkali metal methylate in a reaction mixture containing a small amount of a quinoid hydroxynaphthalene compound, whereby the reduction of the aromatic nitrogen compound is promoted.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 483,368 Rosenstiehl Sept. 27, 1892 2,014,522 Dahlen et a1. Sept. 17, 1935 2,570,866 Sargent et a1 Oct. 9, 1951 

1. THE IMPROVEMENT IN THE METHOD OF REDUCING AN AROMATIC NITROGEN COMPOUND CONTAINING NITROGEN IN A REDUCIBLE FORM AS A NUCLEAR SUBSTITUENT AT A HIGHER STAGE OF OXIDATION THAN THE HYDRAZO STAGE BY THE ACTION OF A METAL ALCOHOLATE, WHICH COMPRISES CARRYING OUT THE REDUCTION IN A REACTION MIXTURE IN WHICH A QUINOID HYDROXYNAPHTHALENE COMPOUND HAS BEEN INCORPORATED, WHEREBY THE REDUCTION OF THE AROMATIC NITROGEN COMPOUND IS PROMOTED. 